The present embodiments relate generally to the field of additive manufacturing and, more particularly, to curing defects and/or creating a single crystal microstructure or columnar grain microstructure in an additively manufactured component.
Additive manufacturing is a process by which parts can be made in a layer-by-layer fashion by machines that create each layer according to a three dimensional (3D) computer model of the part. In powder bed additive manufacturing, a layer of powder is spread on a platform and selective areas are joined by sintering or melting by a directed energy beam. The platform is indexed down, another layer of powder is applied, and selected areas are again joined. The process is repeated until a finished 3D part is produced. In direct deposit additive manufacturing technology, small amounts of molten or semi-solid material are applied to a platform according to a 3D model of a part by extrusion, injection, or wire feed and energized by an energy beam to bond the material to form a part. Common additive manufacturing processes include selective laser sintering, direct laser melting, direct metal laser sintering (DMLS), electron beam melting, laser powder deposition, electron beam wire deposition, etc.
Because a part is produced in a continuous process in an additive manufacturing operation, features associated with conventional manufacturing processes such as machining, forging, welding, casting, etc. can be eliminated leading to savings in cost, material, and time. Furthermore, additive manufacturing allows components with complex geometries to be built relatively easily, compared to conventional manufacturing processes.
However, despite its benefits, additive manufacturing has limitations. One limitation of additive manufacturing is that it is incapable of reliably producing components with a single crystal microstructure or columnar grain microstructure. Rather, an inherent feature of an additively manufactured component is a polycrystalline microstructure. The inability to additively manufacture single crystal or columnar grain components can be problematic. For example, a number of gas turbine engine components generally need to have a single crystal microstructure to withstand high temperature, high stress operating environments (e.g., components located in a hot gas stream). As well, for some gas turbine engine components a columnar grain microstructure can beneficial.
A second limitation of additive manufacturing is quality control of the component being additively built. Generally, component subsurface defects are inherent in additive manufacturing processes. It can take tens of hours (or more) to additively build a component, yet it is inevitable that at least some finished additively built components will have subsurface defects, such as contaminates and/or voids. As a result, such defective components are rejected after spending significant resources in building these components.